Preparation of alkene halides

ABSTRACT

THERE IS PROVIDED A ONE STEP ELECTROLYTIC PROCESS FOR MANUFACTURE OF MONOHALOGENATED ALKENES BY ELECTROLYZING IN AN ELECTROLYTIC CELL AN AQUEOUS SOLUTION OF A METAL HALIDE BETWEEN TWO GAS-PERVIOUS, LIQUID-IMPERVIOUS ELECTRODES. AN OXYGEN-CONTAINING GAS IS IMPINGED ON THE SURFACE OF ONE OF THE ELECTRODES WHILE AN ALKENE IS IMPINGED ON THE SURFACE OF THE SECOND ELECTRODE AND A MONOHALOGENATED ALKENE IS RECOVERED.

J. S. MAYELL PREPARATION ALKENE HALIDES Jan 26, 1971 Filed Feb. 12, 1968INVENTOR. JASPAL SINGH MA YE LL ATTORNEY United States Patent 3,558,453PREPARATION OF ALKENE HALIDES Jaspal Singh Mayell, Stamford, Conn.,assignor to American Cyanamid Company, Stamford, Conn., a corporation ofMaine Filed Feb. 12, 1968, Ser. No. 704,822

' Int. Cl. C0711 9/00 US. Cl. 204-81 9 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to a novel electrolytic process for themanufacture of alkene halides. More particularly, it relates to a methodfor the manufacture of monohalogenated alkenes, such as vinyl chloride,l-chloropropene-l,

1 chloro-Z-methylpropene-1, vinyl bromide and l-chloro-'4-methylpentene-l, in a'one step process utilizing an oxygen-containinggas-depolarized electrode.

In the past, a monohalogenated alkene, such as vinyl chloride, wasproduced by a vapor phase reaction of acetylene and hydrochloric acid toprepare said vinyl halide. Due to safety and economic considerations,however, this method has largely been replaced by a two-step process'o'fmanufacture of vinyl chloride from'ethylene. In-this two' step process,ethylene can be converted to dichloroethylene by either a vapor phasereaction of "ethylene with chlorine or, more recently,'by the oxychlo--rination process where a liquid phase reaction "of ethylene withhydrochloric acid occurs utilizing a cupric-cuprous couple as a catalystin the presence of oxygen. The dichloroethylene made from either methodis then thermally cracked and the resulting product is vinyl chloride.Because both of these ethylene reactions require two distinct chemicalprocess steps, it has been desired to have 'a com- "rnercially feasibleone step process utilizing ethylene to form vinyl chloride. For'similarconsiderations, the same "is true for other monohalogenated alken'es ofthe vinyl It is, therefore, a principal objectof this present inventionto provide *anovel process for'the manufacture of monohalogenat'edalkene compounds from' alkenes. further object is to provide anelectrolytic process for a direct one step process for manufacture ofmonohalogenated alkene compounds. Other objects and advantages willbecome apparent from a consideration of'the followingdetailed-description. 7 v 1 An electrolytic method and cell are provided'so as to obtain from a' brine solution with minimal power expenditure ahalogen, substantially free from hydrogen, which reacts with an alkeneto form the monohalogenated alkenes. In its broadestaspecflthe' methodof the invention contemplates the .use of. an electrolytic cell in which(1) an aqueous metal halide solution as the electrolytic medium, (2) aplurality of gas-liquid electrodes, one of which is oxygen-containinggas-depolarized, (3) an external power source and (4) an alkene, arepresent so that the halogen can react with the alkene to form thedesired product.

A variety of electrolytic cells can be used for effecting the processingof a brine solution according to the process of the invention. One suchcell comprises a container ice which is electrically inert and whichmay, if desired, be provided with any suitable heating means. There isintroduced through a suitable port of the container an aqueous solutionof a metal halide, such as sodium chloride, sodium bromide, potassiumchloride, potassium bromide and equivalent metal halides, usuallyranging in concentration from about 15% to about 30%. The cell is alsoprovided with a gas-permeable and liquid-impermeable positive electrodewhich constitutes the anode and a gaspermeable but liquid-impermeablenegative electrode which constitutes the cathode. In assembling theoverall cell, the respective electrodes are separated from each other bythe electrolyte and electrically linked to an external power source.There is also provided on both the cathode side and the anode side ofthe container liquidimpermeable chambers into which a suitableoxygen-containing gas, such as oxygen or air, is introduced solely forthe purpose of contacting the gas-permeable-liquid-impermeable cathodeand into the anode chamber an alkene gas, such as ethylene, propylene,butylene, isopropylene, B-methyIbutylene-l, pentene, 4-methylpentene-l,and other equivalent alkenes, is introduced solely for the purpose ofcontacting the gas-permeable-liquid-impermeable anode. In operation, thecell, whose contents are maintained at temperatures ranging from 25 C.to about 100 C. and preferably between about C. and 0, forms halogen gasat the anode thereof. This halogen gas passes through thegas-permeable-liquid-impermeable electrode and contacts the alkene inthe anode chamber forming the final product which is withdrawn from thecell. At the cathode side of the cell, oxygen is reduced to hydroxyl ionwhich then reacts with the alkali metal ions in the electrolyte to forman alkali metal hydroxide. During electrolysis, however, hydrogen gas isnot evolved.

The gas-permeable-liquid-impermeable electrodes employed in this processcan advantageously be prepared from an electrically conductive material,such as carbon,

.to which there is added a noble metal or other active metal catalyst.Further, a metallic screen may be impressed on the electrode and asuitable electrical lead then attached thereto. In order to avoid anyelectrolyte flowing into the zone when the oxygen-containing gas isintroduced, the cathode is backed, for instance, with a porouspolytetrafluoroethylene sheet, thereby permitting only theoxygen-containing gas to flow through the electrodes backing. Ifdesired, the cathodes surface fronting on the electrolyte can bemodified with an ion exchange resin membrane, such as, for instance, acopolymer of styrene sulfonic acid on polytetrafluoroethylene and acopolymer of acrylic acid on polyethylene.

Advantageously, the halogen conversion from brine solution requires avoltage range from about 1.1 to about 3.1 volts. This range issatisfactory to maintain an effective difference in potential across thecell. It is found that for best operations there should be establishedan external potential for each cell of between 2.4 volts and about 3.0

volts at a current density of milliamperes per square centimeter. Theinvention will be described in detail in conjunction with the followingdrawing which is to be taken as nonlimiting.

The sole drawing is an exploded view of one embodiment of a possibleelectrical cell, in cross section, which 'may be used in this invention.The halogen produced from permeates through an anode and a porouspolytetrafluoroethylene separator 6 and comes in contact with ethylenewhich enters at port 7, reacting, and the product vinyl chloride iscollected through an exit port 8. The brine solution is in contact withthe positive electrode or anode 5, a negative electrode or cathode 9,and an ion exchange membrane 10'.

In general, the positive electrode 5 is prepared by molding a noblemetal, graphitic carbon or a mixture of graphitic carbon and a noblemetal with a water-proofing agent, such as polytetrafluoroethylene, intoan electrode into which is embedded a tantalum metallic screen 11directly linked to an external power source (not shown) through asuitable wire lead 12. The negative electrode 9 is prepared in a similarfashion as is the positive electrode 5 in which there is embedded atantalum screen 13 connected to the same external power source (notshown) through a suitable wire lead 14. Sealing gaskets 15 and 16 areprovided so as to prevent any leakage of electrolyte. The cathode isbacked by a porous polytetrafluoroethylene 17 so as to allow only gasbut not liquid to permeate through it. There is also provided apolytrifluoromonochloroethylene chamber 18 having an inlet port 19 forintroducing oxygen-containing gas. Any excess or unreactedoxygen-containing gas is permitted to exit through port 20. Spacer 21 isprovided to prevent the buckling of the cathode and also for uniformdistribution of the oxygen-containing gas at the cathode surface. Thechamber 18 is backed by another inert gasket 22. There is also provideda polytrifluoromonochloroethylene chamber 23 having an outlet port 8 forexiting vinyl chloride. An inert, rigid, plastic screen spacer 24 isprovided to prevent the buckling of the anode and also for uniformdistribution of the chlorine gas at the anode surface. The chamber 23 isalso backed by gasket 25. The entire assembly is held in place by endstainless steel plates 26 and 27, secured by bolts and nuts (not shown).There are also provided electrical heating pads 28 and 29 attached toend plates 26 and 27. A thermocouple 30 and a thermistor 31 arepositioned in the chamber 2 to maintain a constant temperature control.

In order to demonstrate the advantages of the process of the presentinvention, the following examples are presented.

EXAMPLE 1 A aqueous solution of sodium chloride is continuouslycirculated in the electrolytic chamber of the electrolysis cell. The twosides of the electrolytic chamber are positioned by twogas-pervious-liquid-impervious graphitic carbon electrodes containingabout 5% polytetrafluoroethylene. Oxygen is allowed to fiow over thecathode surface not facing the electrolyte and ethylene is allowed toflow over the anode surface not facing the electrolyte. The area of eachelectrode exposed to the electrolyte is 20 cm. The surface of thecathode facing the electrolyte is covered with a low resistance Permion1010 ion exchange membrane. The gases coming out from the anodiccompartment are passed through a trap cooled to -40 C.

The solution is electrolyzed for 5 hours and 40 minutes, at 60 C., at aconstant current of 1.0 amperes which is equivalent to a current densityof 50 ma./cm. The solution obtained in the trap weighed 3.03 grams andanalysis by vapor phase chromatography indicated that the solutioncontained vinyl chloride in good yield.

EXAMPLE 2 A aqueous solution of potassium chloride is continuouslycirculated in the electrolytic chamber of the same cell used inExample 1. Air is allowed to flow over the cathode surface not facingthe electrolyte and isobutylene is allowed to flow over the anodesurface not facing the electrolyte.

The electrolytic cell is operated in the same manner as Example 1.Analysis of the solution product shows the presence of1-chloro-2-methylpropene-1.

EXAMPLE 3 A 20% aqueous solution of sodium chloride is continuouslycirculated in the electrolytic chamber of the same cell used inExample 1. Oxygen is allowed to fiow over the surface of the cathode inthe same fashion as described in Example 1 and propylene is allowed toflow over the surface of the anode in the same fashion as described inExample 1.

The electrolytic cell is operated in the same manner as Example 1. Uponanalysis, propylene chloride is found in the resultant solution in goodyield.

Substituting 4-methylpentene-l for propylene and operating the cell inidentical manner as Example 1, the resulting productl-chloro-4-methylpentene-l is found in good yield.

I claim:

1. An electrochemical process for production of monohalogenated alkeneswhich comprises: electrolyzing an aqueous metal halide solution in anelectrolytic cell having a gas pervious, liquid impervious porousmembrane anode through which is passed the halogen gas product of suchelectrolysis and reacting said halogen gas as it emerges from the outersurface of said porous anode with an alkene supplied to said outersurface and recovering monohalogenated alkene product from fluidsremoved from said outer surface of said anode.

2. The process according to claim 1 wherein the alkene is ethylene.

3. The process according to claim 1 wherein the alkene is propylene.

4. The process according to claim 1 wherein the aqueous solution of ametal halide to be electrolyzed is sodium chloride.

5. The process according to claim 1 wherein the aqueous solution of ametal halide to be electrolyzed is sodium bromide.

6. The process according to claim 1 in which the conversion of theaqueous metal halide solution to a halogen occurs at a temperatureranging from about 25 C. to about 100 C.

7. A process defined by claim 1 wherein said process is carried out inthe defined cell which further comprises an oxygen-depolarized porouscathode.

8. The process according to claim 1 in which electrolysis is carried outwith a potential established across the cell from about 1.1 volts toabout 3.1 volts.

9. The process according to claim 1 wherein said electrodes are eachbacked with a porous, unsintered, polytetrafluoroethylene membrane.

References Cited UNITED STATES PATENTS 2,273,795 2/ 1942 Heise et al.204-81 3,288,692 11/1966 Leduc 204 JOHN H. MACK, Primary Examiner R. L.ANDREWS, Assistant Examiner US. Cl. X.R. 204263 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3,55 |53 Dated January 26,1971 Inventor(s) JASPAL SINGH MAYELL It is certified that error appearsin the above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column L line 52, cancel "Claim 1" and substitute Claim 7 Column LL,line 55, cancel "Claim 1" and substitute Signed and sealed this 27th dayof April 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attesting OfficerCommissioner of Patents OHM P0-1050 (10-69)

